The present invention relates to a V-type multi-cylinder internal combustion engine, particularly to a suction manifold of the engine and a variable suction device of the engine for switching over the suction characteristic so as to obtain a high volumetric efficiency over a wide rotative speed region from a low rotative speed region to a high rotative speed region.
In an internal combustion engine for a vehicle, it is desired to reduce rotative speed of the engine for improving fuel consumption or reducing noise on operation. For this purpose, improvement of torque on low speed rotation is necessary, and in order to improve torque on low speed rotation, improvement of volumetric efficiency of suction must be contrived.
In general, it has been carried out that length or volume of a suction pipe of an internal combustion engine is changed in accordance with rotative speed of the engine to maintain a high volumetric efficiency over a wide rotative speed region from a low speed region to a high speed region utilizing combination of inertia supercharging effect and resonance (pulsation) effect of the suction air.
Also in the V-type multi-cylinder internal combustion engine, a construction capable of increasing suction pipe length of a suction manifold in a low rotative speed region is desired. On the one hand, when the suction manifold is provided with a pipe length switchover construction, inertia supercharging effect in a high rotative speed region often undergoes a bad influence, so that a construction having little influence on the inertia supercharging effect in the high rotative speed region is desired.
Further, in order to reduce a rambling noise resulting from unequal lengths of suction pipes measured from a suction sound source, equalizing of the suction pipe lengths including preparation of a surge tank is desired. However, particularly in case of the V-type multi-cylinder internal combustion engine, a clearance must be ensured within an engine room between the engine and a bonnet hood so that degree of freedom of shape of the suction pipe is small.
Simplification of pipes around the suction manifold including a breather pipe and a blow-by gas returning passage (PCV passage) is also desired.
Japanese Laid-Open Patent Publication No. 7-102979 discloses an improved V-type multi-cylinder internal combustion engine which can satisfy the above-mentioned various demands.
The internal combustion engine described in the Japanese publication has manifold suction pipes crossing each other and communicating with respective cylinders in right and left banks opposite to each other in V-shape, and surge tanks of a predetermined volume disposed above the manifold suction pipes. The manifold suction pipes are connected to the surge tanks with sections of J-shape, branch short-circuit passages short-circuiting middle parts of the manifold suction pipes to the surge tanks are opened at an partition wall partitioning the manifold suction pipes and the surge tanks, and branch control valves for opening and closing the branch short-circuit passages in accordance with operation condition are provided. In a communication passage connecting the surge tanks with each other is provided a tank control valve for opening and closing the communication passage in accordance with operation condition.
In the above-mentioned engine of the Japanese publication, entire height of the engine can be restrained sufficiently ensuring length of the suction pipes and volume of the surge tanks. By adequately controlling opening and closing of the branch control valve and the tank control valve in accordance with operation condition of the engine, a high volumetric efficiency can be maintained over a wide rotative speed region from a low speed to a high speed of the engine utilizing combination of supercharging effects based on inertia and resonance.
An internal combustion engine provided with variable valve timing switchover means for switching over suction characteristic of a suction valve and suction passage switchover means capable of switching over characteristic of a suction passage has been disclosed by Japanese Laid-Open Patent Publication No. 1-262317.